1. Field of the Invention
This invention relates to a PCM signal recording system and is more particularly directed to a synchronizing circuit for copying in which reproduced data is transferred to a recording means.
2. Description of the Prior Art
The use of VTRs (Video Tape Recorder) and video disks are known which use an analog signal such as an audio signal which is digitized and recorded and reproduced.
Such recording and reproducing systems are known as PCM recording and reproducing systems and have an advantage for performing high quality copying (termed dubbing) and also greatly improve the noise, and distortion characteristics as well as reduce wow and flutter. In a conventional analog system recorder there is a deterioration of the tone quality for each copying and it is difficult to accomplish high quality copying. On the other hand, PCM recording and reproducing systems allow copying which is free from such deterioration because the copying is done with a digital signal. Also, since PCM recording and reproducing systems generally include data correcting functions, the reproduced digital output to which the error correcting process has been applied can be recorded so that copying with the high quality is possible.
In such PCM recording and reproducing systems, during normal recording, a crystal oscillator is provided to produce a master clock signal which is frequency-divided to produce various clock signals which are necessary for recording. During normal reproduction, the synchronizing signal is extracted from the reproduced PCM signal and used to control a PLL (Phase Locked Loop) circuit that includes a VCO (Voltage Controlled Oscillator) which produces a master clock signal which is frequency divided so as to obtain various clock signals necessary for the reproduction process. When recording or reproducing is independently performed, even if the respective systems are operated with independent clock signals, there will be no problems.
However, when copying is to be performed with the digital signal, the systems must be synchronized since the digital data is transmitted or received between the reproducing and recording systems.
For this purpose, normally a PLL circuit has been provided in the recording system, and a word clock signal of the recording system is phase-compared with a word clock signal of the reproducing system as a reference to obtain synchronization of the recording system with the reproducing system. However, in order to perform synchronization with high accuracy, it is necessary to increase the gain of a DC amplifier to amplify the output of a low-pass filter of the PLL circuit and even microscopic noise influences the VCO which is provided in the PLL circuit and which produces the master clock signal for the reproducing system during copying, and this causes malfunctioning of the reproducing equipment.